1. Field of the Invention
The present invention relates to a portal-type sampling system for sampling the air around vehicles for purposes of detecting trace chemicals present therein.
2. Description of the Related Art
The rise in worldwide terrorism has made it imperative that border traffic security stations and traffic checkpoints screen for concealed explosives as well as performing their normal function of controlling access to certain locations and searching for persons of interest. Experience has shown that concealed explosive devices have been transported onboard vehicles by terrorists on a number of occasions, some of which have resulted in disasters claiming the lives of many persons. Further, the modern terrorist is sophisticated enough to obtain and use plastic explosives, a small amount of which may be sufficient to destroy a building or checkpoint, act as an effective improvised explosive device (IED), or be effectively used to attack military and civilian vehicles and convoys, and which are very difficult to detect.
It is well-known that specially-trained dogs can detect such concealed explosives under the proper circumstances, despite the fact that the concentration of explosive in the air may be as little as a few parts per trillion. Chemical detection devices of exquisite sensitivity have also been developed, based on the principles, for example, of mass spectrometry, ion-mobility spectrometry, or gas chromatography. Very effective devices are shown, for example, in U.S. Pat. No. 5,200,614 that issued to Anthony Jenkins and in U.S. Pat. No. 5,491,337 that issued to Anthony Jenkins and William J. McGann. Commercialized detectors that incorporate the technology of U.S. Pat. No. 5,200,614 and U.S. Pat. No. 5,491,337 typically function by initially rubbing a wipe over an article, such as a piece of luggage, that is likely to carry a trace amount of a composition of interest. The wipe then is placed in an apparatus employing the technology of U.S. Pat. No. 5,200,614 or U.S. Pat. No. 5,491,337, and an air stream is directed through the wipe to transport trace amounts of molecules of interest into the apparatus for detection. A wipe cannot realistically be rubbed across the entire body of a vehicle to test for substances of interest. Therefore, what has been lacking in the prior art is a rapid, convenient, effective means for such sensors to sample the intimate environment of vehicular subjects to screen for concealed explosives.
A hand-held sensor attached to one of the detection devices mentioned above has been used in the prior art to carry out a scan of a vehicle. Such a device is marketed by Nomadics®, Inc. of Stillwater, Okla. under the trademark “FIDO.” Some of the technology in this device is disclosed in U.S. Pat. No. 6,558,626. This type of device can be used effectively at vehicle border crossings for detecting the presence of certain explosives, chemical weapons, or narcotics. However, this prior art device would be very time-consuming when applied to the many thousands of vehicles, which pass borders and checkpoints each day, and would be perceived as an intrusive approach which would be likely to elicit objections if used on a significant proportion of those vehicles.
Less intrusive means of screening for concealed explosives have been proposed. As explained in U.S. Pat. No. 6,073,499 issued to Settles, many of these proposals are fundamentally flawed in assuming that the proper method for sampling vapors and particles is to disturb those particles horizontally, or vertically downward. As eloquently explained by Settles, rising from human subjects is a thermal plume. Efficient collection of particles and vapor from a human subject should be performed by leveraging this thermal plume.
Similarly, although not taught by Settles, nor demonstrated in the art, rising from most operating vehicles is a thermal plume. This plume carries dirt, dust, pollen, other particles, and vapor both from the surface of the vehicle and from the interior of the vehicle. This plume has a substantially larger volume than that produced by a person and typically rises much faster than that produced by a person.
Settles references U.S. Pat. No. 4,964,309 issued to Jenkins et al. and observes that particle and vapor sampling systems for human subjects based on air-curtains dilute samples as much as 100,000-fold, that the flow rate cannot be effectively reduced, and that Jenkins solution is “saloon-doors” which make contact with the body and which through suction sample air from intimate contact with the subject. There are several practical problems with a contact solution for sampling from vehicles. Nevertheless, the dilution problem is acute for any particle and vapor collection system, especially when such collection is from a large object, instead of the relatively small object, a person, contemplated in Settles.
Settles expresses that the referenced and above-described prior art perceived a need to strip, scrub, or otherwise dislodge explosive vapors and/or particles from the skin and clothing of human subjects. These vapors and/or particles are presumed to be stagnant and to require active disruption and removal in order to provide a sufficient signal to an explosives-detection analyzer. Further, Settles notes that air currents used in the prior art for purposes of dislodging particles from human subjects are generally oriented horizontally with respect to the vertical orientation of a standing human subject, or at least are not oriented vertically.
As does Settles, we observe that the prior art for sampling portals that avoid physical contact, whether for sampling from human subjects, vehicles, or other subjects, rely upon the movement of very large quantities of air compared to the thin layer of air surrounding the subject. This leads to a very great dilution of the chemical traces released by a subject with concealed explosives. Given such dilution, the task of detecting a vanishingly low concentration of explosive or other chemical trace in a large mass of air becomes essentially an impossible one. Further, the prior art devices generally sample only a small portion of the airstream they create. Since available explosive analyzers can accept only a very small sample size, most of the generated airflow is not examined at all for the presence of trace explosives. Solid particulates are not specifically sampled or, if they are, they are subsequently boiled off to present a gaseous sample to the chemical analyzer. This heating must be done carefully to avoid decomposing the very compounds one is looking for.
Settles notes that the prior art recognizes that some combination of explosive vapor and/or particulates is or may be involved in the proper functioning of an explosive-detection portal. It is further asserted that such portals have broader applications, i.e. in drug and hazardous-materials detection as well. Finally, it is noted that the functions of explosive detection and metal detection, as for concealed weapons, may be integrated into a single portal-type device.
However, neither Settles nor the prior art addresses the additional difficulties of sampling from vehicles. First, the fluid dynamics of a portal large enough to contain a vehicle is more complicated that the fluid dynamics of a small portal containing a human subject. The shape of a vehicle is typically vastly more disturbing to the flow of heated air around it, and substantially complicates the flow pattern in the portal. The temperature of the vehicle, especially in and around the engine compartment is substantially higher than that of a typical human subject, producing both more and hotter thermal plume than for a human subject. This plume rises more rapidly and can thereby more readily induce turbulence in its own motion. Thus we find that the prior art does not adequately teach the efficient capture of particles and vapors from a vehicle.
Further, in Settles, we find teachings related to the emission of skin particles by human subjects. As is evident to one knowledgeable in the art of many fields, including machinery, metal working, and biology, vehicles do not have an epidermis, and do not release flakes of skin into the environment. However, as one knowledgeable in the art of forensics knows, the exterior surface of most objects, perhaps especially vehicles, is covered with dirt, dust, pollen, adsorbed particles and vapors, and other “contaminants” that are characteristic of the environment and materials to which the vehicle has been exposed. These contaminants are constantly exchanging with the environment so that at any instant, contaminants that were previously on the vehicle's surface are liberated into the environment near the car, especially to the layer of air that flows to form the vehicle's thermal plume. Similarly contaminants from the environment are constantly arriving at and adsorbing to the surface of the vehicle. Thus, although the mechanism is different from that of human subjects, a vehicle is constantly exchanging contaminant material with its local environment.
We find, as does Settles that the role of the exchange of these contaminants for detecting trace contamination is not adequately taught in the prior art. Further, we find no evidence in the prior art that the exchange of contaminants between the surface of a vehicle and its surroundings has been taught. Since the feasibility of detecting materials of interest is directly related to capturing the material and passing that material to sensing device, clearly accounting for the vehicular thermal plume and the exchange of contaminants with the environment is a substantial component of successfully screening vehicles.
Finally, we find in the market a dearth of products suitable for the detection of vapors or particles of substances of interest. At this time, vehicle screening portals for radiological detection are essentially the only screening options available. Sandia National Laboratories has demonstrated a drive-through trailer, roughly the size of an ISO container, which contains a shroud that is lowered onto the driver-side window of an automobile and which draws air through the shroud to a sampling apparatus. In all cases, the vehicle is driven into the portal and stopped. For radiological detection, the driver and other occupants are required to leave the vehicle. For the Sandia screening device, roughly two to three minutes is expended positioning the vehicle to be properly fitted by the shroud and then an additional 30 seconds is required to sample vapors. In all cases, the current art shows no evidence of drive-through vehicle screening portals nor of portals that can be passed in very short time, such time necessary to satisfy the throughput requirements of a border crossing or a traffic checkpoint.